Unloading and relief valve



J. M. TOWLER ET AL UNLOADING AND RELIEF VALVE Oct. 20, 1953 Filed Aug. 24, 195o z-U mmf causieva FL'nv-cwgk C D-lathovvffuaev" CHT-romy/ Patented Oct. 20, 1953 UNLOADING AND RELIEF VALVE John Maurice Towler, Rodley, and Frank Hathorn Towler, Doh Park, near Otley, England, assignors to Electraulic Presses Limited, Rodley, England, a corporation of England Application August 24, 1950, Serial No. 181,172

4y Claims.

The present invention relates to a new and improved unloading and relief valve.

One of the objects of the present invention is to provide an unloading and relief valve which is operative automatically to pass a relatively large aggregate volume of pressure fluid from a plurality of sources and, as the volumetric requirements are reduced, to unload part of these sources and to sustain the pressure developed by the remaining part of these sources.

A more specific object is to provide an unloading and relief valve which is operable to receive pressure uid from two sources, to combine the delivery from the two sources during relatively low pressure conditions, to unload one of these sources through by-passing the delivery thereof upon a predetermined increase in the developed pressure, and to sustain the pressure developed bythe other source at a predetermined peak level through a relief valve action.

A further object is to provide a unitary valve ofthe foregoing character which is simple and inexpensive in construction, and eicient and reliable in operation.

Other objects and advantages will become apparent as the description proceeds.

In the accompanying drawings:

Fig. 1 is a side elevational view of a valve embodying the features of the present invention.

Fig. 2 is a longitudinal sectional view of the valve taken substantially along line 2-2 of Fig. 1.

Figs. 3 and 4 are transverse sectional views taken respectively along line 3-3 and 4-4 of Fig. 2.

Fig. 5 is a simple diagrammatic representation of the valve of Fig. 1 operatively connected in a hydraulic transmission circuit.

Referring more particularly to the drawings, the combined unloading and relief valve, constituting the exemplary embodiment of the present invention, comprises a valve body I formed with two separate inlet passages II and I2, a pressure delivery passage I3 and an exhaust passage I4. The passages II and I2 are adapted for connection respectively to two sources of pressure fluid. Preferably, one of these sources has a relatively large volume capacity or output, and the other has a relatively small volume capacity or output. For example. the valve of the present invention may be used very advantageously with a dual pump I having relatively large and small displacement pump units integrated in a unitary or self-contained structure, but having a common intake conduit I6 and independent delivery conduits I1 and I8. These pump units constitute pressure fluid sources of the foregoing character, and are connected through the conduits I1 and I8 respectively to the valve inlets II and I2.

The details of construction of the dual pump I5 are not directly related to the present invention, and hence are not fully disclosed herein. Briefly stated, the pump I5 takes fluid through the conduit Iii from a sump I9, and comprises a plurality of parallel annularly-arranged plungers (not shown) reciprocable through the action of a wobble plate (not shown). The plungers of the annular series are alternately large and small in diameter, the large plungers delivering fluid to a manifold connected with the conduit I1 and hence constituting the large displacement unit, and the small plungers delivering fluid to another manifold connected with the conduit I8 and hence constituting the small displacement unit. More particularly, the pump I5 is of the form disclosed in our copending application, Serial No. 122,698, filed October 21, 1949, to which reference may be had for a more complete understanding.

Referring back to the valve body I0, the inlet passage I2 is in constant communication with the delivery passage I3, and the inlet passage II is adapted for connection therewith through a check valve 20. The delivery passage I3 is adapted for connection through an outlet conduit 2| to that portion of the hydraulic system in which the fluid is to be utilized for performing work. In the simple system herein shown for illustrative purposes, the conduit 2I is connected to a direction control valve 22 which is adjustable to direct the pressure fluid selectively through either one of two conduits 23 and 24 to the related end of a motor cylinder 25, and to pass uid from the other end of the cylinder through the other of the motor conduits to a drain conduit 26 leading to the sump I9. A piston 2'I is operatively reciprocable in the cylinder 25 and has an axial piston rod 28 projecting therefrom for performing work. The hydraulic motor 25, 21 may be utilized for actuating machine elements having heavy duty requirements, as, for example, the movable head of a large press (not shown).

The unloading and relief valve of the present invention also comprises valve means including a movable valve element 29 which is normally biased into one extreme position to cause the full delivery of fluid from both passages II and I2 to the passage I3, but which is operable, in response to a progressive pressure rise in the latter passage, rst, at a predetermined adjustable pressure designated for convenience as P1, to connect the passage II to the exhaust passage I4, thereby unloading the delivery of the large-volumedisplacement unit of the pump I5, and then, at a higher predetermined pressure designated for convenience as P2, to relieve excess uid from the passages I2 and I3 to the exhaust passage, whereby to limit the pressure in the system. The passage I4 is adapted for connection to a conduitI 30 which may lead to any suitable point of fluid disposal, such as the sump I9.

It will thus be evident that the valve is operative to pass the entire delivery of both uid sources as long `as the volumetric requirements of the system remain large, then to by-pass the major portion of this delivery without the excessive expenditure of energy when these requirements are substantially reduced, and finally to relieve the remaining portion of this delivery to whatever extent is necessary to limit the top working pressure as these requirements are further reduced or satisfied.

Within the broad aspects of the invention, the valve, and its various component parts, may be of any suitable form or character. In the preferred form, the valve body Ill comprises a rectangular block having a bore 3I, with a counterbore 32 in one end, opening therethrough, and having the passages II, I2 and I4 formed therein transaxially of, and in axially spaced relation along the bore 3I. The passages II and I2 are parallel and located in a common plane, and the passages II. and I4 are open at their inner ends through ports 33 and 34 to the bore 3I. A rectangular block 35, formed with the delivery passage I3, is bolted to the underside of the block I in position to close one end of the bore 3I, except for a port 36 opening from the passage to the bore.

The body block I is additionally formed with a bore 31 parallel to the bore 3l and constituting the chamber for the check valve 20. This bore 31 opens to the delivery passage I3, intersects with the passage I2, and connects through a conical valve seat 38 at one endwith the passage II. A tubular guide sleeve 39 is mounted coaxially within the bore 31, and is formed on theouter periphery :at opposite ends with circumferentially-spaced locating lugs 4G permitting the free passage of fluid thereabout from the passages II and I2 to the passage I3. The lugs 40, at one end engage the seat 38, and at the other endv are engaged by a holding ring 4I. A joint ring 42 is snugly interposed between the ring 4I and the delivery block 35 so that the latter serves to maintain the parts in assembly. The check valve 20 comprises a valveV member 43 having a stem 44 slidabli7 guided in one end of the sleeve 39, and normally engaging the seat 38. The other end of the sleeve 39 is closed, except for a vent opening 45, and a coiled compression spring 46 disposed therein tends to urge the valve member 43 outwardly into seated position.

A valve bushing 41 is tightly tted within the bore 3I, and has a peripheral locating fiange 48 on one end seating in the counterbore 32. A joint ring 49 is interposed between the ange 48 and block 35 to hold the parts in assembly. The bushing 41 has an axial valve bore 50 opening therethrough, and three axially-spaced sets of radial ports I, 52 and 53 opening to the bore. The set of ports 5I communicate with an outer peripheral groove 54 in the bushing 41 in registration with the port 33 of the passage II. The other two sets of ports 52 and 53 communicate with an outer peripheral, groove 55 in the bushing 4 41 in registration with the port 34 of the pasd sage I4.

A valve plunger 56 is slidably adjustable in the bore 56. One end of the plunger 56 projects into a counterbore 51 in communication through the port 36 with the pressure passage I3. This end of the plunger 56 normally seatsyagainst a ball 58 in the counterbore 51., and is formed with a peripheral recess 59 movable into communication with the ports 53 to provide for pressure relief. 'Iwo small bores 60 intersect opposite sides of the counterbore 51 to provide a free path of flow about the ball 58 so that the end of the plunger 56 is constantly exposed to the pressure of the fluid in the passage I3. Intermediate its ends, the plunger 56 is formed with a wide peripheral recess 6I always open to the ports 52 and movable into communication with the ports 5I to establish the by-pass for unloading the passage I I.

The other end of the valve plunger 56 projects from the bushing 41and is subjected endwise to the action of a coiled compression spring 62 normally maintaining it inabutting engagement with the yball 58 in which position it blocks the flow of uid through the bore 50. The recesses 59 and 6I are so located that in the continued movement of the plunger 56 in response toa rising pressure gradient in the counterbore 51 acting against the force of the spring 62, the recess 6I will open to the ports 5 I before the recess 59 opens to the ports 53.

The spring 62 is suitably enclosed in an oil filled casing 63 bolted on the body I0 in axial alignment with the valve bore 50. The spring 62 is interposed between and in abutting engagement at opposite ends with two retainer pads 64 and 65. One of these pads, e. g. the pad 64 is slidable in the lowervend of the casing 63 andV has an axial seating recess 66 engaging the contiguous end of the valve plunger 56. The other pad 65 has a centering depression 61 engageable by the conical end of a stem 68 on an adjusting screw 69.. The stem 68 extendsslidably and rotatably through a guide bushing 16 into a tubular projection 1I on the free end of the casing 63. The screw 69 extends through and is in threaded engagement with an outer end wall 12 of the projection 1I. A hand knob 13 is iixed, as by means of a set screw 14, to the outer end of the screw 69 and affords means for turning the latter to adjust the pressure of the spring 62 at will to suit the required operation. The knob 13 is provided with a micrometer screw 15 whichtelescopes with the tubular projection 1I and coacts with a suitable scale 16 on the latter to indicate the degree of adjustment. A stop washer 11, on the end of the projection 1I., is engageable by the inner face of thev knob 13 to limit the degree of adjustment, and may be provided in different thicknesses so as to permit selective variation of the limit of adjustment.

The operation will be evident from the foregoing description, and briefly summarized is asr follows.: Assuming that the motor 25, 21 is utilized for operating the ram of a press, the pressurefiuid from both units of the pump I5, suppliedthrough the passages II` and I2, will be delivered through the passage I3 to advance thev ram inA a rapidv approach movement. As the ram encountersy increasing working resistance, the pressure in the passage I3 will rise,'and this will' ordinarily be accompanied by a reduction` or elimination o-f rram movement with a. corresponding reduction in volumetric fluid requirement. Consequently,` as the fluid pressure inthe rising gradient reaches the predetermined value Pi, the valve plunger 56 will move out of idle position against the force of the spring 52 to interconnect the ports 5I and 52 through the recess 6I and thereby fully unload the passage II to the exhaust passage Ill. Thereupon, the check valve will be maintained closed, and only the fluid from the passage II will be supplied to the delivery p assage I3. The fluid thus available from the small volume unit will be sufficient to actuate or hold the press ram as may be required. Upon continued rise in the iiuid pressure to the predetermined valu'e P2, the valve plunger 56 will be displaced still further to interconnect the delivery passage I3 and exhaust passage I4 through the recess 59 and thereby provide fluid relief. The relief passage will be opened more or less to pass such part or all of the available fluid as may be required to establish a state of equilibrium between the fluid pressure and the spring force, thereby sustaining the pressure P2 as a holding force.

The pressure values P1 and P2 are susceptible of relative variation by selective spacing of the recesses 59 and 6I in relation to the ports 53 and 5i. For example, if the recesses 59 and 5I are arranged to open substantially simultaneously to the ports 53 and 5I, the pressures P1 and P2 will be substantially coincident and determined in amount by the adjusted force of the spring 52. If the recesses 55 and 6I are arranged to open successively but in close sequence to their respective ports 53 and 5I, the difference between pressures Pi and P2 will be small, viz. on the order of 200 to 300 p. s. i. This arrangement is well suited for sustained pressure operation in which the large volume source is unloaded and the small volume source is blown oil through the relief valve to the extent required to sustain the pressure. Alternatively, the control edges of the recesses 59 and 60 may be spaced so widely that a large pressure difference will be obtained, viz. on the order of 2000 to 3000 p. s. i. This arrangement is well suited for two-stage pressure operations.

The valve of the present invention is especially advantageous for use with the dual pump I5 having two delivery outlets. II" desired, the valve body i0 may be mounted in gasketed relation directly on the pump casing in position to locate the valve passages II and I2 in immediate registration with the pump delivery ports. ln such arrangement, the conduits Il and I8 would not be required to be in the form of interposed tubes or passages, and hence within the meaning of i the present disclosure, any reference to the conduits Il and I8 is to be taken as meaning broadly any flow connections establishing intercommunication between the valve and its iluid sources.

Within the specic aspects of the invention, not only is the valve well suited for use with the dual pump I5, but the valve and pump when used together constitute a variable delivery source of pressure fluid advantageous for the widely varying uid volume and pressure requirements of press operations.

We claim:

1. An unloading and relief valve comprising a body having two separate inlet passages, a pressure delivery passage in constant communication with one of said inlet passages, a cross passage connecting the other of said inlet passages to said delivery passage, and an exhaust passage, a check valve interposed in said cross passage for passing fluid directly from the other of said inlet passages to said delivery passage, and valve means at the down-stream side of said cross passage responsive to the pressure in said delivery passage, said valve means normally blocking said other inlet passage from the exhaust passage and operable upon a predetermined rise in said pressure to connect saidother inlet passage to said exhaust passage, said check valve alone being operative to prevent fluid flow through said cross passage upon operation of said valve means, and said valve means being operable upon `a further predetermined rise in said pressure to relieve said delivery passage to said exhaust passage.

2. An unloading and relief valve comprisinga body having a valve bore and rst, second and third sets of ports opening at axially spaced points to said bore, a delivery passage in communication with' one end of said bore and having an inlet adapted to be connected to one source of pressure fluid, a second passage in communication with the rst set of ports and having an inlet adapted for connection to another source 0f pressure fluid, and an exhaust passage in communication with saidpsecond and third sets of ports, a valve member slidable in said bore and exposed lat one end to the pressure in said delivery passage, said end of said plunger having a peripheral recess movable into communication with said third set of ports to provide a pressure relief connection between said delivery passage and said exhaust passage, said plunger being formed intermediate its ends with a peripheral recess always in communication with said second set of ports and movable into communication with said iirst set of ports to unload said second passage to said exhaust passage, adjustable compression spring means acting on the other end or said plunger in a direction to bias said plunger in opposition to the pressure in said delivery passage whereby to move said recesses out of communication with said rst and third sets 0f ports, and check valve means for passing fluid directly from said second passage to said delivery passage when said rst set of ports is blocked.

3. An unloading and relief valve comprising a body having a bore and first and second sets of ports opening at axially spaced points to said bore, a delivery passage in communication with one end of said bore and having an inlet adapted to be connected to one source of pressure fluid, a second passage in communication with the first set of ports and having an inlet adapted for connection to another source of pressure fluid, and an exhaust passage in communication with said second set of ports, a valve member slidable in said port and exposed at one end to the pressure in said delivery passage, said plunger having a first peripheral recess always in communication with said delivery passage and movable into communication with said second set of ports to provide a pressure relief connection between said delivery passage and said exhaust passage, said plunger being formed with a second peripheral recess always in communication with said exhaust passage and movable into communication with said first set of ports to unload said second passage to said exhaust passage, adjustable compression spring means acting on the other end of said plunger in a direction to bias said plunger in opposition to the pressure in said delivery passage whereby to move said recesses out of communication with said sets of ports, and check valve means for passing uid from said second passage to said delivery passage when said lrst set of ports is blocked by said valve member.

4. An unloading and relief valve comprising in combination, a body having a valve bore, an exhaust outlet, a pressure delivery outlet always open to one end of bore, a first fluid pressure inlet always open to said delivery outlet, a second fluid pressure inlet having port means in said bore, and a cross passage opening from said second inlet at a point ahead of said port means to said. delivery outlet, a valve plunger slidable in said bore, means normally biasing said plunger in one direction for movement progressively first to block said port means and then to block said delivery outlet from said exhaust outlet, said plunger being exposed at one end to the pressure prevailing in said delivery outlet for movement in response torsaid pressure on a rising gradient progressively first to connect said port means to' said exhaust outlet and then said delivery outlet to said exhaust outlet, and a normally closed check valve interposed in said cross passage and operable to permit now from said second inlet to said delivery outlet when said port means is blocked by said plunger.

JOHN MAURICE TOWLER. FRANK HAIHORN TOWLER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,951,398 Dearsley Mar. 20, 1934 1,982,711 Vickens Dee. 4, 1934 2,549,897 Evrell Apr. 24,V 1951 

